This invention relates generally to a screening apparatus for separating solid materials by size. More particularly, this invention pertains to an improved grizzly screen apparatus for separating rocks, concrete, asphalt and other objects by size.
A separation apparatus known as a xe2x80x9cgrizzlyxe2x80x9d or xe2x80x9cgrizzly screenxe2x80x9d has been known for many years. Such screens comprise a series of strong, parallel, spaced apart bars that are used to separate large rocks and other debris from material of smaller size Such screens provide a relatively coarse size separation and are typically used to separate oversize rocks from smaller materials, such as in a gravel plant, a road construction project or quarry.
Typically, a grizzly screen will utilize parallel steel bars which are in a fixed position relative to each other and be spaced about 4-6 inches apart. Thus, the grizzly apparatus will separate rocks and other materials having a dimension greater than the bar spacing from smaller sized materials passing through the screen.
As unsorted debris is dropped onto the screen, objects which are smaller than the bar spacing slip between the bars into a receiving bin, flume, truck or conveyer. Objects larger than the bar spacing cannot slip between the bars and will roll and/or slide to the lower end of the screen and fall therefrom. The plane of the grizzly bars may vary depending upon the application, but is typically at an angle of about 20 degrees to encourage such rolling and sliding of the larger objects.
A major problem with grizzly screens is that objects having at least one dimension only slightly larger than the bar spacing tend to become jammed between the bars of the screen. These obstructions prevent or retard the discharge of subsequently encountered objects, and the screening capacity increasingly deteriorates. Often such jammed objects require manual removal from the screen using a crowbar, sledge hammer and the like.
It is known to manufacture a grizzly screen whose bars have tapered cross-sections wherein the bottom of each bar is narrower than the top, thus increasing the likelihood that objects passing downward through the screen will not become jammed between the bars This innovation does not, however, prevent all jamming of the screen and serious jamming problems still occur.
It is desirable to reduce the amount of manual contact which an operator must devote to the removal of jammed obstructures from the grizzly screen. Typically each removal effort requires the operator to remove four to six inch or larger rock from the bars with a heavy crowbar or sledge hammer, and any reduction of such manual clearing work decreases the risk of accident or injury. In addition, some materials sorted by the screen may be of a toxic nature, and it is desirable to reduce manual handling of and close operator exposure to such materials as much as possible.
Still a further shortcoming of existing grizzly screens is that the bars forming such screen are usually rigidly connected to the screen frame and require considerable effort and tools to remove or replace damaged or worn bars. It is desirable to provide a positive attachment apparatus for the screen bars which also allows easy removal and replacement of the bars without tools.
An object of the invention is an improved grizzly screening apparatus which effectively provides for rapid and easy removal of oversize materials which become jammed between the grizzly bars and obstruct the screen.
An additional object of the invention is a grizzly screening apparatus which has a reduced down time for dislodging obstructions from the screen.
A further object of this invention is a grizzly screening apparatus having a controllable movement whereby obstructions may be freed without manual intervention with tools.
Another object of the invention is a grizzly screening apparatus in which obstructing objects may be removed without significantly changing the separation or tolerance characteristic of the screen.
Another object of the invention is a grizzly screening apparatus in which worn or bent bars may be easily and quickly replaced with minimal use of tools.
A grizzly screening apparatus includes left and right side frame members which are interconnected by a transverse end member and at least one transverse crossbar fixed to the side frame members. Mounted on the frame and comprising a screen are a plurality of parallel solid metal, circular cross-section grizzly bars. Each grizzly bar has a first end which is pivotally held in a passageway in the transverse end member and so positioned therein as to prevent its unintended removal. The opposite, free ends of the grizzly bars interact with a stationary transverse comb member which comprises a vertically slotted horizontal member. The comb member has alternating deep bed and shallow bed slots into which the second ends of the grizzly bars are received. The grizzly screen is typically positioned above a receptacle such as a bin, flume, truck or conveyor. The screen is pivotable about a horizontal axis near its discharge end so that its transverse end member and the first ends of the grizzly bars attached thereto may be pivotally moved between a sorting position and a raised clearing position.
In the sorting position, where the screening operations are conducted, all of the grizzly bars have their second ends at about the same elevation, i.e. all grizzly bars are supported by at least one crossbar and are positioned near the upper ends of the slots of the comb member to about the same depth, in the comb member slots, regardless of the slot depth. In the raised clearing position, the second ends of some grizzly bars engage the shallow slot beds of the comb member while the second ends of other grizzly bars drop to a lower level in the deep slots. Thus, the second ends of the grizzly bars diverge from one another in elevation and spacing distance as the screen is pivoted upwardly to the clearing position. The second ends of the grizzly bars are held within the deep bed slots and shallow bed slots, and thus each bar moves in a vertical plane. As the screen moves from sorting to clearing position, the horizontal spacing between the adjacent grizzly bars remains essentially constant, while the actual spacing between bars increases as the second ends of the bars diverge as the angle of the screen with the horizontal is increased.
The pivot axis of the grizzly screen is so located toward the second ends of the grizzly bars that pivotal movement of the screen upwardly from a lower position results in engagement of some of the grizzly bars with the bottom of the shallow slots of the comb member, while alternate grizzly bars continue to drop to a lower level in the deep slots. As a result, the bars in the deep slots have their second ends lower than bars in the shallow slots, and the actual spacing between the second ends of adjacent bars increases. Because of this vertical bar movement and the accompanying increase in spacing, obstructions caught between the grizzly bars will come loose from the bars and roll or slide off the screen or pass through the screen, depending upon the size of the obstructing object. The increase in actual spacing is relatively small, so that the object rejection size or tolerance is not significantly changed. The simultaneous increase in slope and spacing of the grizzly bars results in enhanced rolling and sliding of obstructing materials from the screen, quickly and efficiently clearing objects from the screen.
The screen may be pivoted about the pivot axis by a hydraulic cylinder, electric motor or other device capable of lifting the screen. Any of these motive means may be equipped with a remote control device by which an operator may clear obstructions from the screen without leaving a front end loader or other vehicle.
The invention also includes a novel means for attaching the grizzly bars to the screen frame to provide positive retention of the bars, and to allow an operator to remove and quickly replace damaged or worn bars without tools.
These and other objects and advantages of the invention will be readily understood by reading the following description in conjunction with the accompanying figures of the drawings wherein like reference numerals have been applied to designate like elements throughout the several views.